Fossils
There are many ways that fossils can be formed; here is a quick breakdown of some of the ways. We tend to think of fossils as being made up of stone, like dinosaur bones, but the term can be also used to describe the preservation over millennia of creatures and plants in other ways. Here is some information which will broaden your understanding of what a fossil is.
Fossilising by Freezing (refrigeration)-This is the best means of preservation of ancient materials fully, and only usually happens to animals. It happens only rarely. The animal must be continually frozen from the time of death until discovery. That means it only applies to cold hardy animals from the last ice age. There have been several discoveries of mammoth and wooly rhinoceros for example, found in ice from Alaska and Siberia. Specimens with flesh, skin, and hair intact have been found. Some of these finds suggest that they were flash frozen, with food still in the mouth and stomach.
Fossilisation by Drying (desiccation)- Mummified bodies of animals including humans have been discovered in very dry environments like sever deserts. These are places where it never rains and there is very little or no air moisture. The soft tissues including skin and organs are preserved for thousands of years if they are completely dried. Again like the fossilisation by freezing the item must be kept in this completely dry state form death to discovery.
Fossil imprints-Imprint fossils are rock casts of the original material. To make a fossil imprint, something must have died and been buried. The organics then decay away, but the impression they left in the sediments below and above are preserved. To form these types of fossils, the buried object must have been covered by a flood or died in a lake or perished in some way that allows for water to flow over it- with sediments- soon after death. You can have imprint fossils in sandstone, siltstones and claystones as well as other stones. To get the best and most highly detailed impressions, however, you'll need a finer grained material such as siltstones and clays as they often give the best imprint fossils.
Fossilisation in Asphalt- In what is now downtown Los Angeles lies a 23 acre park called The La Brea Tar Pits, also known as Hancock Park. Within the park are over 100 pits filled with sticky asphalt or tar. The tar pits were formed by crude oil seeping through fissures in the earth. The lighter elements of the oil evaporate leaving thick sticky asphalt. The pits are famous for the number and high quality of Pleistocene fossils that have been pulled from the pits. The fossils date between 10 and 40 thousand years old. Asphalt is an excellent preservative. Bones, teeth, shells, the exoskeletons of insects, and even some plant seeds have been pulled from the pits.
Fossilisation in Amber- Insects, spiders, and even small lizard have been found, nearly perfectly preserved in amber. This occurs when an insect is trapped by the sticky sap that the tree has made to protect itself from fungal infection. As the insect struggles to escape it becomes more and more entombed in the sap until it is completely engulfed and suffocates. The tree eventually dies and falls into the swampy water from which it grew. Over the course of millions of years the tree along with countless others becomes a coal deposit and the sap with our insect inside is polymerized and hardened into amber.
Fossilisation by Carbonization (distillation)- In this process of fossilisation plant leaves, and some soft body parts of fish, reptiles, and marine invertebrates or plant life decompose leaving behind only the carbon. The rest of the elements are removed. This leaves only the carbon and it creates an impression in the rock outlining the fossil, sometimes with great detail.
Fossilisation by Permineralization-This is the most common method of fossil preservation. Minerals fill the cellular spaces and then crystallize. The shape of the original plant or animal is then preserved as rock. Then the original material is dissolved away leaving the form and structure but none of the organic material remains. This means the shape of the original thing is retained but none of the original plant or animal.
No matter which way preservation occurs it takes a lot of luck, pure happenstance. Most living things are quickly recycled upon death. Scavengers and bacteria usually consume all but bones and shells.
Still millions of fossils have been found. If you think about all of the museums, university palaeontology labs, fossil dealers, and private collectors, there really are a lot of fossils that have been discovered! However when you think of the billions and billions of living things that have inhabited the earth over the last 550 million years only a very small percentage are immortalized in stone!
So to some questions;
- Look carefully at the rocks used to line this drive and describe what you can see in terms of fossils.
- One rock about half way along has a very clear fossil imprint, larger than your hand; tell me what was fossilised here?
- Look at the information above and tell me what type of fossilisation took place to leave this discovery, explain your reasoning.
- Finally tell me how many rocks are here lining the drive.
Thanks for visiting the location, I hope you can find the fossils and I look forward to reading your logs.